The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Not applicable.
(1) Field of the Invention
The present invention relates to a high sensitivity fiber optic rotation sensor.
(2) Description of the Prior Art
A microbend fiber optic sensor gives changes in the intensity of transmitted light in response to changes in fiber curvature. As curvature increases (bend radius decreases), a portion of the light traveling through the fiber is lost through dispersion and diffraction through the fiber wall. Fibers are used as sensors by measuring the change in transmitted light intensity. The physics of intensity based fiber optic sensors using microbends was first published by G. Zeidler, A. Hasselberg, and D. Schickentanz in their paper: xe2x80x9cEffects of Mechanically Induced Periodic Bends on the Optical Loss of Glass Fibersxe2x80x9d, Optics Communications, Vol. 18, pp. 553-555, 1976. These investigators demonstrated the loss of intensity due to bending a fiber between a pair of plates with meshing, corrugated surfaces. Increasing the curvature by moving the plates together increased transmission loss.
An alternative configuration, the figure eight topology, was developed in 1993 at the University of Rhode Island by Sienkiewicz, Shukla, Letcher, Sing and Zhou in their paper: xe2x80x9cOn the Use of Microbend Fiber Optic Sensors in Material Characterizationxe2x80x9d, SPIE, vol. 2072, pp. 214-233. These configurations use a tightening of the curvature of the fiber to increase the intensity loss of the fiber. One such figure eight sensor is shown in U.S. Pat, No. 4,358,678 to Lawrence.
These prior art sensors have relatively low sensitivity and require cumbersome loading fixtures.
Devices for sensing a degree of rotation for angular disposition are known in the art. For example, U.S. Pat. No. 4,633,079 to Rieger illustrates a sensor for measuring the degree of articulation of finger joints in a remote underwater vehicle. The sensor uses a length of an optical fiber connected to each finger joint. As the joint is rotated, the bending of the optical fiber changes the attenuation of light through the fibers and a detector monitoring this change provides a signal that is correlated to the degree of articulation.
U.S. Pat. No. 5,274,226 to Kidwell et al. illustrates a single optical fiber which is used to measure angular or rotational position in a rotary sensor. The optical fiber is used in connection with known analog intensity optoelectronics and with a microbending device housed within the sensor. An input shaft of the sensor experiencing rotational motion causing the microbending device to subject the optical fiber to microbending. Microbending can be caused by a loading arrangement such as a crankpin, pins located on the shaft within the housing, or a transverse hole located through the shaft. A micrometer lead screw can be used within the housing to convert the rotational motion into linear motion. The converted linear displacement is used to compress the optical fiber. Where the input shaft experiences many rotations or multiple turns, the linear displacement can be applied to a spring element carrying a load or force to a compression device. Microbending experienced by the optical fiber causes a change in the fiber radius of curvature. These microbending losses are then measured by the optoelectronics or photodetection arrangements.
U.S. Pat. No. 4,436,995 to Whitten illustrates a transducer for sensing the magnitude of a parameter, such as mechanical displacement/motion, pressure, temperature, electrical voltage, and current, which uses a multimode optical waveguide fiber. At least one portion of the fiber is subjected to bending in an amount changing with a change in the sensed parameter magnitude. The resulting microbending losses in the fiber vary the attenuation of light energy between an optical source and an optical detector.
U.S. Pat. No. 4,552,026 to Knudsen et al. illustrates a fiber optic device for sensing the generation of vortices by measuring the torsional displacement of a bluff body mounted for rotation about its center of inertia within a fluid conduit. An internally toothed member is fixed to the outside of the fluid conduit, and an externally toothed member is fixed to the bluff body for rotation therewith and is in partial meshing relation to the externally toothed member. An optical fiber is entrained between the toothed members and has one end exposed to a light source and the opposite end connected to a detector which is operable to detect changes in the intensity of the light transmitted through the fiber. As the bluff body vibrates, the toothed members are displaced relative to one another causing changes in the radius of curvature of the segments of the optical fiber received between the teeth, thus changing the intensity of light transmitted through the fiber in proportion to the changes in the radius of curvature.
U.S. Pat. No. 5,260,566 to Reed illustrates a sensor which includes an optical fiber sensor which has a microbend module engaged thereto. When the module is subjected to external influences such as pressure and displacement, it places microbends in the sensor fiber which changes a light transmission characteristic of the fiber. Light passing through the sensor fiber is detected, and changes in the light are measured to find the influence on the modulator.
U.S. Pat. No. 4,891,511 to Reed illustrates a fiber optic microbend sensor with a braided arrangement of multiple optical fibers such that the length dependent microbending losses result from the interaction of the fibers themselves without the need for additional external structures such as corrugated plates.
U.S. Pat. No. 4,734,577 to Szuvhy illustrates a fiber optic load measuring system which comprises a light source, a fiber optic attenuator, a photodetector, and a signal processor. The fiber optic attenuator was formed to have a curved portion along the length thereof disposed in low transfer relation with the surface where the load is measured. The signal processor is adapted to receive signals from the photodetector and measure variations attributable to the application of a load on the surface. The processor is further adapted to linearly translate the detected variations to compute deformation of the curved portion in response to an applied load.
U.S. Pat. No. 5,134,281 to Bryenton et al. illustrates an optical sensor comprising an optical fiber having a core covered by a cladding, the cladding having an index of refraction different from that of the core, apparatus for retaining the fiber in a sinuously looped disposition, apparatus for fixing the fiber to an object to be sensed whereby movement to be sensed results in one or both of according expansion and contraction of loops of the fiber and microbending of the fiber, apparatus for applying a first optical signal into one end of the fiber, apparatus for detecting a resulting optical signal from the other end of the fiber, and apparatus for comparing the first and resulting optical signals to obtain an indication of the movement.
U.S. Pat. No. 5,193,129 to Kramer illustrates a pressure detector having a fiber optical cable woven through a ladder like structure which is then encapsulated and surrounded by a cover. Light transmitted through the fiber optic cable is diminished to a value less than a threshold value upon the occurrence of microbending caused by pressure applied at any location along the length thereof. The rungs of the ladder like structure are sized and spaced to provide a proper locus about which microbending may be produced.
Despite these various types of optic fiber sensors, there remains a need for a sensor which provides very high output sensitivity for low physical or rotary input.
Accordingly, it is an object of the present invention to provide a rotation sensing device which provides very high output sensitivity.
It is a further object of the present invention to provide a rotation sensing device which does not require cumbersome loading fixtures.
The foregoing objects are attained by the fiber optic rotation sensing device of the present invention.
In accordance with the present invention, a fiber optic rotation sensing device is provided. The fiber optic rotation sensing device broadly comprises a stationary base, a rotatable member, and an optical fiber configured in at least one loop about the rotatable member. The optical fiber is affixed to an exterior portion of the rotatable member and to the base. Rotation of the rotatable member causes a distortion of the at least one loop in the optical fiber and a change in the intensity of the light passing through the optical fiber. The change in light intensity is measured to provide an indication of the degree of twist of the rotatable member.
Other details of the fiber optic rotation sensing device of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.